The present invention relates to a process for amorphous growth with local crystallization under coherent electromagnetic radiation. It makes it possible to obtain thin semiconductor crystalline layers.
Several conventional crystallization methods are known. The simplest method is thermal annealing, which consists of heating the film obtained by amorphous growth on a substrate. In the case of silicon, the heating temperature is approximately 800.degree. C. This method has the advantage of being simple, but has the disadvantage of leading to twin crystals forming in the layer. Moreover, this method is of an overall or total nature and is less flexible than local crystallization or recrystallization methods.
There are also methods using photocrystallization, such as recrystallization by scanned or pulsed laser beams, which perform the local recrystallization of a layer by heating. The disadvantage of this is that the temperature reached at the impact point of the laser beam on the growth film is often above the melting temperature of the element or substance constituting said film. This leads to differential expansion stresses between the heated area and the area surrounding it. This leads to numerous defects in the film, such as cracks and microscopic faults which are responsible for leakage currents. However, these methods relate to an annealing, in this case local, on layers of materials which have already been deposited.
A process using evaporation is also known, namely the molecular jet process, which is based on the principle of evaporation under an ultra-high vacuum, i.e. under a pressure of 10.sup.-7 to 10.sup.-9 Pa on the basis of Kundsen effusion cells. On the basis of this cell, it is possible to obtain a relatively directional jet of molecules or atoms in order to epitaxially cover a relatively small surface.
This procedure leads to a very thin layer epitaxy (a few angstroms) and whose thickness is well controled. ln this way, it is possible to prepare compounds ayer by layer. However, its main disadvantage is that it requires an ultra-high vacuum, so that it is complicated and costly. Therefore, the costs involved in obtaining layers by this procedure is generally incompatible with mass production.